My computer is a HP Pavilion P6000 series, and the model number is P6115Y. Here's what is does (or doesn't do, depending upon how you look at it).
When you turn it on, as it's loading up, the bios on the motherboard finds all the stuff (hard drive, CD drive, etc.) it's supposed to, however, when Windows Vista begins to load, it can't find any of that and says it can't load. You go back to the bios, and it can't find it. You reboot the bios (you switch one of the dip switches for 15 seconds and then the bios finds everything) and then begin to load Windows and it can't find anything and you check bios and it can't find anything. You can repeat this over and over (although I don't know why you'd want to).
You can try the hp recovery program if you've burned it to a dvd. Or you can try a spare hardrive. I've had bad motherboards prevent windows from loading due to a worn capacitor, but they're too expensive to get someone else to replace. You'd have to inspect them and replace them yourself. In other words, do some basic troubleshooting and try some spare parts.